Various devices (e.g. headphones, earbuds, behind the ear devices, hearing aids, and other devices that direct acoustic energy into an acoustic measuring device (e.g., ear)) have been designed for various uses. Many conventional systems have difficulty sealing in the ear canal. Other orifice (e.g., ear, mouth, anus, nose, artery, vein, pipe, indentation) insertion devices additionally have sealing issues. Various methods of sealing can impact the orifice walls. The amount of impact is important for designing comfortable orifice sealing devices.
With regards to ear devices, many fitting difficulties result from ear dimensional changes, for example during chewing. For example some articles have reported (e.g., ten years of research and development sponsored by The National Institute on Deafness and Other Communication Disorders (NIDCD) have resulted in a better understanding of ear canal dynamics relative to jaw motion) both contraction or expansion of the ear canal volume during jaw motion. It has been reported that substantial numbers of ears have significant shape and size changes with jaw motion, that 51% of subjects have at least one ear canal in which the volume expands or contracts at least 10% with jaw opening, that 12% of subjects have at least one ear canal in which the volume contracts more than 10% with jaw opening, and that only 15% of the population have both a symmetric magnitude and direction of volume change in their canals. Such volume changes cause comfort issues with fitted hearing aids and other devices fitted in the ear canal.
A sample market with associated issues is the hearing aid market. It is estimated that more than 20 million people in the United States experience some form of hearing loss. However, according to the 1990-91 National Health Survey, only 18% of those who identified themselves as having hearing problems use hearing aids (over the age of three and non-institutionalized). The reasons people who experience hearing loss but chose not to use the available technologies include: “hearing aids do not perform in noisy situations” (7.1 million), “provide too much whistle or feedback” (6.4 million), “do not work well” (4.8 million) or “work only in limited situations” (4.3 million), “have poor sound quality” (3.9 million), “break down too much” (3.4 million), “can not be used on the telephone” (3.1 million), and “negative experiences of friends” (3.9 million) (Kochkin, 1997). Custom hearing aids first use an ear mold of the user's ear canal.
Many hearing aids start with a silicon mold of the ear canal, then are scanned and placed into a computer model. The computer model serves as an ear canal. Then a hearing aid is fabricated by trimming the model to form an earmold shell smaller than the ear canal, into which electronics are placed for a hearing aid. The earmold shell provides several basic functions. First, it couples the hearing aid with the user's ear. It channels the sound from the hearing aid, through the ear canal, to the eardrum. The earmold shell also helps to secure the electronics of the hearing aid in place. The challenge is to provide the user with a secure fit (i.e., a small distance between the earmold shell and the ear canal). Yet the tighter the fit, the more uncomfortable the device is to wear. A well-fitted earmold shell directs sound from the hearing aid to the ear without feedback, thus allowing the user to hear comfortably (Lachapelle, 1999), however the tradeoff is comfort. Earmold shells are required for most hearing aids that fit within the ear canal, and since the anatomical structure of the ear varies from person to person, the majority (80%) of all earmold shells are custom-made.
Feedback (e.g., between the microphone and receiver) is an issue with hearing aids. Feedback is experienced by 6.4 million hearing aid users. There are two types of acoustic feedback: (1) produced internally from the hearing aid, indicating a need for repair; and (2) the more common cause, externally produced feedback due to leakage of amplified sound, that radiates from the speaker and then is picked up by the microphone and re-amplified. In many cases, the feedback can be addressed by either repositioning the hearing aid or by reshaping the earmold so that its fit conforms more closely to the shape of the ear canal (Smedley & Schow, 1998; Sweetow, 1998).
Feedback occurs when the hearing aid does not fit properly and the output signal leaks around the earmold, is received by the hearing aid microphone, and is amplified. Other causes of feedback include the vents that are drilled into them. Vents are used to reduce the “plugged up” feeling experienced when the user speaks. However, the vent also provides an opening for the sound to create feedback within the hearing aid. At high amplification the output signal can again be picked up by the hearing aid microphone and be amplified. Users who experience significant feedback will adjust the hearing instrument's gain, or will turn it off completely. In the worst-case situation, the hearing aid user will stop wearing the device altogether.
There is a need to improve the comfort of earmolds while maintaining the secure fit necessary for proper hearing aid function, including the reduction of acoustic feedback. Chewing, yawning, and other facial movements change the geometry of the ear canal structure. As the anatomic structure changes, the fit of the earmold is affected causing an increase in acoustic feedback. The hearing instrument may dislodge from the ear if the ear canal's shape is changed.